The object of this study is the clarification of the role of membrane-bound iron-sulfur centers in the basic bioenergetic processes of energy-transducing systems. The role of membrane-bound iron-sulfur centers in electron-transfer and energy conservation reactions will be investigated. The basic analytical technique will be electron paramagnetic resonance (EPR) spectroscopy at cryogenic temperatures where iron-sulfur centers have characteristic resonance signals. One iron-sulfur protein (the Rieske center) has been found in association with the b- and c-type cytochromes in mitochondria and its presence will be sought in situ in other energy-transducing systems. A complex analogous to mitochondrial Complex III will be isolated from other membrane electron transfer systems and the components essential for ATP synthesis will be defined. The possible role of the Rieske iron-sulfur center as a proton carrier during energy conservation will be tested in order to test its function in the chemiosmotic model of energy transduction. The relationship of multiple bound iron-sulfur centers to known enzymic functions and to electron transfer pathways of chloroplasts and chromatophores will also be considered. After isolation and characterization, these bound proteins will also be used in experiments attempting to reconstitute the electron transfer and energy conservation processes.